In Ref.[1]} Transverse Momentum Conservation (TMC) is derived and
demonstrated that if there is no other correlation in the data except
elliptic flow TMC will give a negative
\(\langle cos(\phi _1 + \phi _2 - 2\Psi _{RP}) \rangle \)  (\(\gamma \) ) which is
\(v_2\)  smaller than \(\langle cos(\phi _1 - \phi _2) \rangle \)  (\(\delta \) ).
\(\delta \)  is a negative number given by TMC and scales as 1/N (N is the number
of particles). Also in Ref.[1]} Local Charge Conservation (LCC) is
another important background and the details of LCC is found in
Ref.[3]}. The authors of Ref.[3]} point out that for
same sign pairs LCC should give a small negative sign, while for opposite sign
pairs LCC should give a large positive correlation. Using the same coupling
effect to the reaction plane as TMC, one should expect
\(\langle cos(\phi _1 + \phi _2 - 2\Psi _{RP})_{+-} \rangle \)  (\(\gamma \) ) equal \(v_2\) 
times \(\langle cos(\phi _1 - \phi _2)_{+-} \rangle \)  (\(\delta \) ) for the LCC.
